Male sexual development and function is dependent on androgen stimulation of its cognate receptor and subsequent activation of gene expression. Androgen receptor (AR) is activated by hormone and transduces a cellular response by binding to specific DNA sequences located in target genes and recruiting basal transcriptional machinery to activate transcription. This recruitment process is regulated by accessory proteins that serve as signaling mediators between AR and other transcription factors. The main objective of this work is to identify proteins in androgen-responsive tissues and cells that regulate androgen- dependent gene expression. This will be accomplished by completing the following specific aims: 1) Identify coactivator and corepressor proteins that interact with the N-terminal transactivation region of the human androgen receptor; and 2) Characterize androgen receptor coregulatory proteins to determine their role in androgen receptor-mediated gene transcription. The AR N-terminal transactivation domain will be used as bait in a newly developed yeast two-hybrid system to screen cDNA libraries prepared from human epididymis and testis tissue and two prostate cancer cell lines. Proteins identified by the screen will be evaluated for in vitro and in vivo interactions with AR and also assessed for their influence on the stimulation of an androgen- responsive reporter gene by AR. The identification of AR- specific coactivators or corepressors will provide better understanding of how the AR and other steroid receptors recognize the same DNA response elements yet show specificity of gene activation.